1. Field of the Invention
The present invention relates to an asymmetric lens and a street light including the asymmetric lens, and more particularly, to an asymmetric lens that reduces dazzle while increasing uniformity ratio of illuminance and coefficient of utilization (CU), and a street light including the asymmetric lens.
2. Description of the Related Art
Generally, lighting such as a street light is vertically installed along either side of a street to supply, at night, light onto the street or the surrounding area. Conventionally, a sodium (Na) lamp, a mercury (Hg) lamp, and a metal halide lamp have been generally used for the lighting. However, those conventional lamps consume a great deal of electricity, have a short use life, lead to a high cost for maintenance and repair, and also cause environmental pollution.
Therefore, a light emitting diode (LED) in the lighting is epoch-making in the field of lighting. The LED refers to a semiconductor device that emits light when a current flows. Due to a long lifespan, low power consumption, high response rate, and excellent initial driving characteristics, and the like, the LED is widely applied to various fields including a lighting apparatus, an electric sign, a back light unit of a display device, and the like. Also, the number of fields the LED is being applied to is increasing.
The LED has an excellent light quality in terms of a spectrum of light emitted from an LED light source, and a high emission efficiency and energy saving efficiency. Therefore, at present, the LED is being used widely for lighting of a street light. Outdoor lighting such as the street light using the LED generally collects light rays by a lens mounted to a cover of the lighting. However, a conventional circular lens has a circular light field in which brightness is greatly different between a center and a periphery.
Furthermore, in practical use of the LED lighting, a light range needs to be increased in a certain direction and decreased in another direction.
For example, in a case of street lighting, the light range and the lighting efficiency need to be high in an extending direction of a street. Also, a lighting angle needs to be great. However, in a direction perpendicular to the street extending direction, the light range needs to be low such that wasting of electricity and light pollution are reduced.
When an LED street light applying a conventional circular lens is used, a large number of lights are installed on the street extending direction so as to achieve a desired lighting effect.
In this case, light fields overlap between neighboring lights, thereby increasing brightness. However, since distribution of light intensity is not uniform, the light fields shown on the street may alternate repetition of a bright portion and a dark portion, that is, in the form of ribs. That is, the brightness is high only right under the light but low in the other positions, thereby causing a low average brightness and non-uniform brightness of the street. This may confuse a driver on the street and may even cause a traffic accident. That is, the non-uniform and low brightness of street lights may seriously affect driving safety and cause traffic accidents.
Moreover, in various outdoor and indoor environments aside from thoroughfares, stray light may cause pollution to the surrounding and a dazzle problem.